During the past year, we investigated OCT (optical coherence tomography) imaging as functional measurements of retinal activity and photoreceptor degeneration. OCT has been widely used as a non-invasive tool to provide optical sections of biological tissues. Because the optics of the eye allows for high resolution of retinal structure, OCT is often used in the diagnosis and monitoring of retinal disease progression in the clinic and the laboratory. As OCT technique uses infrared light in generating image, it also provides a useful tool to study light-induced changes in the retinal structure and thickness. Using ultra-high resolution OCT system, we examined light-dependent OCT responses (outer retina length changes under light- and dark-adapted conditions) in a degenerative mouse (rd10) retina. Based on OCT images, rd10 mice could be divided into three degeneration stages: Stage I (P26-29) had no apparent subretinal fluid, Stage II (P32-38) exhibited subretinal fluid in restricted fundus area, and Stage III (P44-45) with extensive subretinal fluid. Compared with wildtype, Stage I rd10 retina had significant thinning in total retina thickness and outer retina length (from outer limiting membrane to Bruchs membrane), indicating large photoreceptor degeneration. Over-night dark-adaptation induced significant shortening of outer retina in wildtype mice (4.61.4m, n=16), but this light-dependent OCT response is much smaller in Stage I rd10 (1.50.5m n=14). Dark-adaptation removed large amount of subretinal fluid for Stage II rd10 mice, and consequently, light-dependent OCT responses were much larger (8.51.5m n=43). In addition, there is a good correlation between light-dependent OCT response and the length of outer retina under light-adapted condition. The effects of dark-adaptation on Stage II rd10 mice were confirmed using both Bioptigen UHR-OCT and Spectralis HRA+OCT systems. However, dark-adaptation was ineffective to change subretinal fluid observed in large area of Stage III rd10 mice. Keeping rd10 mice in complete darkness from P6-30 significantly prevented retinal degeneration compared with those reared under normal lighting conditions. In conclusion, our study indicate that OCT image is a very useful tool in monitoring fluid dynamics in subretinal space. Retinal degeneration significantly diminished light-dependent OCT responses, indicating importance of photoreceptor function in regulating subretinal fluid dynamics. Eyes with retinal degeneration, such as Stage II rd10 mice, are capable to remove mild subretinal edema by intrinsic mechanisms. However, large subretinal fluid accumulation observed at late stage of retinal degeneration overwhelms intrinsic capacity of the eye. Better management of subretinal fluid dynamics in retinal degeneration eyes could prolong vision in those subjects.